In service station environments, fuel is delivered to fuel dispensers from underground storage tanks (UST), sometimes referred to as fuel storage tanks. USTs are large containers located beneath the ground that hold fuel. A separate UST is provided for each fuel type, such as low octane gasoline, high-octane gasoline, and diesel fuel. In order to deliver the fuel from the USTs to the fuel dispensers, typically, a submersible turbine pump (STP) is provided that pumps the fuel out of the UST and delivers the fuel through a main fuel piping conduit that runs beneath the ground in the service station. Other types of pumps other than a STP, such as a self-contained pump within the dispenser housing for example, may be employed.
Due to environmental and possible regulatory requirements governing service stations, the main fuel piping conduit is usually required to be double-walled piping. Double-walled piping contains an inner piping that carries the fuel. An outer piping forming an outer annular space, also called an “interstitial space,” surrounds the inner piping so as to capture and contain any leaks that occur in the inner piping, so that such leaks do not reach the ground. An example of double-walled fuel pipe is disclosed in U.S. Pat. No. 5,527,130, incorporated herein by reference in its entirety.
It is possible that the inner piping of the double-walled fuel piping could fail, thereby leaking fuel to the interstitial space of the double-walled fuel piping. Or, it is possible that the outer piping of the double-walled fuel piping could fail thereby leaking fuel captured in the interstitial space. In either scenario, without monitoring of the double-walled fuel piping interstitial space, it is possible that a leak in the double-walled fuel piping will go undetected for some period of time. The STP will continue to operate as normal, drawing fuel from the UST; however, the fuel may leak to the ground instead of being delivered to the fuel dispensers.
Recent proposed changes in state and federal regulations will tighten the requirements to contain leaks and will further require better leak detection so that environmental damage may be minimized. As a result, it is becoming imperative that all potential leak sources be evaluated and steps taken to detect and contain leaks in the piping systems.
Methods of monitoring the interstitial space of fuel piping are disclosed in U.S. Patent Application Publication Nos. 2004/0045343; 2004/0149017; and 2004/0182136, which are all hereby incorporated by reference in their entireties. In these systems, a vacuum-generating source, which may be the STP, draws a vacuum in the interstitial space. Thereafter, the interstitial space is monitored for pressure changes. If sufficient pressure changes occur, this is an indication that either the inner piping or the outer piping of the double-walled fuel piping has incurred a leak or breach. The leak or breach could have occurred in any branch or zone of the fuel piping in which the interstitial space is being monitored.
Double-walled fuel piping is located outside of the fuel dispenser beneath the ground in conduits that deliver fuel from the STP to the fuel dispensers. Main fuel piping delivers fuel underneath the fuel dispensers. Double-walled branch fuel piping, typically located within a dispenser sump located beneath ground under individual fuel dispensers, connects the individual fuel dispensers to the main fuel piping to receive fuel for dispensing through its respective hose and nozzle. However, as illustrated in FIG. 5 of U.S. Pat. No. 5,713,607, incorporated herein by reference in its entirety, the interstitial space of the double-walled branch fuel piping, or riser pipe “PR” terminates on the inlet side of the shear valve “VS”. Therefore, the interstitial space, if monitored, is only monitored to a point that stops before the inner fuel piping couples to the shear valve.
Fuel dispensers also contain internal fuel piping or conduits that carry the fuel from the outlet side of the shear valve through various components, such as valves and meters, internal to the fuel dispenser before the fuel exits through the hose and nozzle into a vehicle fuel tank. This dispenser internal fuel piping is not double-walled fuel piping; however, the internal fuel piping can incur a breach as well. If this internal fuel piping is not contained and monitored, the leak can continue to occur without notification, and the STP will continue to operate as normal, drawing fuel from the UST and possibly leaking fuel to the ground. A solution to this issue is provided in U.S. Patent Application Publication No. 2004/0261504, which is hereby incorporated herein by reference in its entirety (hereinafter the “'504 application”).
In the '504 application, a double-walled shear valve is provided between double-walled branch fuel piping located beneath the fuel dispenser and double-walled fuel piping located internal to the fuel dispenser so that the interstitial space of the branch fuel piping is coupled to the interstitial space internal fuel piping for monitoring of breaches or leaks in the fuel piping. Further, by providing a secondarily contained shear valve, the interstitial space around the shear valve can be monitored for breaches or leaks as well.
Therefore, as discussed in the '504 application, it may be desirable to provide secondary containment of the internal fuel piping to the fuel dispenser so that breaches that occur in the internal fuel piping are also contained. Further, it may be desirable to monitor the secondary containment space of the internal fuel piping so that breaches that occur in either the inner or outer fuel piping are detected for the reasons stated above. However, any fuel piping, fittings or couplings, such as the shear valve for example, that are not secondarily contained provide a failure point in the system where a leak will not be contained.
Further, if it is desirable to use the same vacuum generating source that draws a vacuum in the main and/or branch fuel piping interstitial space as the vacuum generating source to draw a vacuum in the interstitial space of the internal fuel piping, the interstitial space of the internal fuel piping must be fluidly coupled to the interstitial space of the branch and/or main fuel piping. Otherwise, a separate vacuum generating source will be required.
Therefore, the present invention provides a double-wall contained shear valve to solve one or more of the aforementioned problems which are also disclosed in the '504 application. The first problem is that fuel that leaks at the shear valve will not be contained even if the branch fuel piping located on the inlet side of the shear valve, or the internal fuel dispenser piping located on the outlet side of the shear valve, is double-walled piping. A double-walled shear valve must be used that still shears properly in the event of an impact even with double-walled containment. A double-walled contained shear valve can provide an interstitial space around the inner housing of the shear valve for monitoring any leaks or breaches in the inner or containment housings of the shear valve for the reasons stated above. The third problem is that the shear valve's fuel flow path should be closed in response to a leak to prevent further leakage.